Real-time in situ ellipsometry for the controlled deposition of anti-reflection coatings on semiconductor laser facets

An innovative technique based on real-time in situ ellipsometry is used to demonstrate the precise monitoring and control of both the refractive index and the thickness of antireflection coatings on semiconductor laser facets.; The configuration and calibration of the ellipsometer are described. A new method for in situ determination of the incidence angle of the ellipsometer is developed for calibrating the incidence angle before each coating process. The entrance and exit windows of an ellipsometer mounted directly on an e-beam evaporator are modeled as waveplates with small retardation to account for the small polarization change due to the residual strain in the windows.; Control of the refractive index of the deposited coating is accomplished by an ellipsometer which is able to extract the refractive index and the layer thickness every 0.5 second using two thin-film models: a conventional four-medium model which provides an average refractive index over the total deposited film, and an adaptive multilayer model which keeps track of all the previous thin layers that have been deposited and provides a sensitive and instantaneous response to any new refractive index change. Using the weighted average of the refractive indices obtained with these two techniques as a feedback parameter, control of the average refractive index of SiO{dollar}sb{lcub}rm x{rcub}{dollar} deposited films to within {dollar}pm{dollar}0.01 or better is reproducibly obtained.; The film thickness is controlled either by ellipsometric measurement of those layers, or by monitoring of the optical power from the laser diode being coated with the last deposited layer.; Reflectivities of order 10{dollar}sp{lcub}-4{rcub}{dollar} or lower are reproducibly achieved for single-layer and various multi-layer antireflection coatings. The facet reflectivity is extracted by fitting the wavelength dependence of the amplified spontaneous emission with the standard expression describing the transmission of a Fabry-Perot with gain. The bandwidth, the tolerance of the coating parameters, and the stability of coatings are addressed. Future extensions of this work are also discussed.